Motors generate substantial heat during operation. In general, either motor output or durability can be improved by efficiently removing heat from the motor or motor enclosure. For example, an electric motor, such as a brushless, permanent magnet motor, operates when an electric current is passed through the conductive windings which are wrapped around the motor stator. The electric current flow is resisted by the winding which results in heat being emitted from the windings and stator poles into the enclosure. In addition, heat is generated from the friction of various motor parts and connections, such as the bearings and output axle. Often motors fail because one or more motor components reaches too high of a temperature and is damaged. For example, a common failure mode for electric motors is when the motor windings get too hot and the protective insulation that surrounds the motor windings partially melts. If the winding is damaged, the electric motor will develop an electric short. This is commonly referred to as a motor “burn out” or “burn up”. While the windings are designed to generate acceptable heat during normal motor operation, they can get too hot as a result of either too much current flowing through the winding (motor overload) or as a result of the air temperatures surrounding the windings getting too hot. This second condition is especially a problem when the motor is located inside a motor enclosure. However if this motor heat can be efficiently removed from the winding region of the motor than usually either the electric motor can be run at a higher speed or load if desired.
Efficiently removing heat from an electric motor is a significant technical obstacle, especially when a motor (stator and rotor) is located within a motor enclosure. Because of the concern for heat removal, electric motors are often marketed and sold based on the type of heat removal system they use. There are two main categories of motors and motor enclosures: open and totally enclosed (TE). Each enclosure name refers generally to how the electric motor is cooled. Open enclosures generally allow air to have direct contact with the motor parts through one or more openings in the enclosure. Typically, if the motors are used outside, the electric motor must be protected from water. These types of motors are commonly called open drip proof (ODP) motors. In an open drip proof motor, the motor enclosure generally has some ventilating opens at the bottom of the enclosure. The openings are arranged so that there is very limited motor contact with water, such as only a drip. These open drip motors are cooled by having cooler air from outside the enclosure continuously flow into and out of the enclosure thus removing the heat from inside the enclosure. This can be accomplished by attaching one or more blades to the shaft so that air is circulated or agitated within enclosure when the electric motor turns the shaft.
Totally enclosed (TE) motor enclosures generally prevent the free exchange of air between the inside and the outside of the motor enclosure. These motors often run at much higher temperatures than motors housed in open enclosures. Of course even though the enclosures are called totally enclosed, they are not air tight. There are several types of totally enclosed motors, each with their own motor cooling scheme. They generally include the following: totally enclosed fan cooled (TEFC), totally enclosed air over (TEAO), totally enclosed air to air (TEAA), totally enclosed pipe ventilated (TEPV), totally enclosed water air (TEAW), and totally enclosed non-ventilated (TENV).
TEFC motors are cooled by an external air fan that is generally mounted on the motor enclosure. The fan is generally away from the output shaft at the opposite end of the motor. The fan blows ambient air, air that is cooler than the air inside the motor enclosure, across the outside surface of the motor enclosure to transfer the heat from inside the enclosure to the surrounding air. TEAO motors are located in an air streams, such as in Heating, Ventilation, and Air Conditioning (HVAC) systems. The motor and enclosure are place in a location where the air moved by the HVAC system passes over the motor enclosure and cools it. TEAA motors are cooled by circulating air inside the enclosure through a heat exchanger. The heat exchanger is in turn cooled by circulating external air across the heat exchanger. These enclosures are thus called air-to-air enclosures. They typically have one or more fans for circulating ventilating air. TEPV motors typically have enclosures with openings arranged on the enclosure for inlet and outlet ducts or pipes. The inlet allows air from outside the enclosure to be brought into the enclosure. The outlet allows hot air from inside the enclosure to be expelled to the surrounding air. They typically have one or more fans for circulating ventilating air. TEWA motors are cooled by circulating air inside the enclosure. The air is first cooled through a water heat exchange. Typically the water-cooled heat exchanger cools the ventilating air and one or more fans circulate the ventilating air inside the enclosure.
TENV motors have no means for internally cooling the enclosure or the motor located inside. The motor or enclosure is cooled by radiating heat from the exterior surfaces of the enclosure to the surrounding air atmosphere. TENV motors are generally small motors, typically less than five horsepower. Thus the surface area of the motor and motor enclosure must be large enough to radiate or transfer the heat via its surface area to outside air without the aid of an external fan or air flow. A special type of TENV is an explosion proof (XP) motor or a motor housed within an explosion proof enclosure. The U.S. Bureau of Mines has applied the term “explosion proof” to motors or enclosures constructed to prevent the ignition of gas surrounding the motor by any sparks, flashes, or explosions of gas or of gas and coal dust that may occur within the motor. The term “explosion-proof casing” or “enclosure” means that the enclosure is constructed to prevent any sparks, flashes, or explosions of gas that may occur within such enclosures from igniting any gas or explosive material surrounding the enclosure. At the same time the enclosure is constructed to retain the motor parts within the enclosure during an explosion. In addition, the enclosure must also prevent ignition of gas or vapor outside the enclosure as well. Thus the motor is designed so that an explosion of flammable gas inside the motor enclosure will not ignite flammable gas outside. In addition the motor fitting, motor, switch, and or fixtures must be contained within the enclosure or in explosion proof containers so that no spark, electric arc, or heat from inside the motor will initiate an explosion in the surrounding environment.
Electric motors are generally used in mining and in explosion environments such as gas and petroleum refinement and distribution. The motors are required to be housed in explosion proof enclosures. As discussed above, these enclosures increase the amount of heat that the electric motors must withstand. Conventional electric motors and enclosures in explosion susceptible environments use one or more of the conventional heat removal techniques described above. FIGS. 1A and 1B illustrate a conventional motor cooling system 100 for an explosion proof environment. The enclosure 10 is representative of a totally enclosed enclosure as described above. The conventional system 100 is illustrated using a fan 14 to blow surrounding or external air over the exterior of the motor enclosure 10. This is commonly referred to as a totally enclosed fan cooled (TEFC) motor cooling system. The motor 20 (represented by dashed lines in FIG. 1B only) is located completely inside the enclosure 10. The fan 14 is located on one end of the enclosure 10. The motor output shaft 16 is located at the other end 11. The electrical box 12 for the motor 20 is illustrated secured to the exterior of the enclosure 10. Heat that is generated inside the enclosure 10 by the motor 20 and the various system components, such as stator windings and friction in the bearings and shaft, is dissipated by radiating the heat through the surface of the enclosure 10. The fan 14 is designed to force sufficient volumes of air over the enclosure 10 to remove the heat from inside the enclosure 10. The heat is removed by convection and radiation, in that the surrounding air is cooler than the surface of the enclosure 10. While this example has been shown with a fan 14, it is to be understood that any of the above conventional cooling systems could also be used in combination with the motor. The motor 10 also requires a controller or regulator that is illustrated as being in electrical communication with the electric box 12. They are conventionally located outside of the motor enclosure 10 since they generate substantial heat during motor operation. This is an obvious disadvantage of conventional systems. By locating the controller separate from the motor, then the system requires a separate enclosure as well as a heat removal system for the controller. Of course in explosion sensitive environment, the controller must also been located in an explosion proof container.
One skilled in the art will understand the obvious disadvantages in using fans or heat exchangers in a conventional motor or motor enclosure cooling systems. First they add to the cost and complexity of making the motor. Second, they require energy to operate the cooling system, fans etc, and labor to maintain and repair the cooling system.
However the passive conventional heat removal system described above, such as a totally enclosed non-ventilated or TENV motor also has many obvious disadvantages. First, it requires an enlarged enclosure and or motor surface area. This enlarged area is necessary to have sufficient surface area to radiate heat from within the motor or enclosure to the surrounding environment. Second, a TENV has a limited heat removal capacity or removal speed therefore motor size or operating loads must be restricted to reduce the amount of heat generated. Thus TENV cooling arrangements are not functional for motors with limited surface area that radiate heat poorly or high output motors that generate substantial amounts of heat. Third, this conventional system is generally not suitable for induction motors where the rotor as well as the stator generates substantial heat deep inside or away from the exterior surface of the motor enclosure. Four, not locating the motor controller inside the explosion proof enclosure increases cooling system cost. Conventional systems require an expensive second enclosure and heat removal system to house the controller. In addition they have the added expense of length electrical cables that must be run from the controller to the motor. The cables can result in electromagnetic compatibility (EMC) problems and can reduce the power output of the motor. Finally, if the motor or controller requires replacement, the repair technician must take the additional repair time to make sure that the controller and motor are compatible.
What is needed is an improved method and system for efficiently removing heat from a motor or motor enclosure, such as a totally enclosed motor enclosure. What is also need is an efficient heat removal method and enclosure design that would allow the controller to be located in the same explosion proof enclosure as the motor.